1. Field of the Invention
This invention relates to the art of cooking foods in microwave ovens, and particularly to the design of a shelf for placement in the bottom portion of the oven cooking cavity to support containers of food to be cooked.
2. Description of the Prior Art
Most microwave ovens are furnished with microwave energy at a frequency of 2450 MH.sub.Z, which is a particular type of high frequency radio energy. The energy enters the cooking cavity at the top in the form of invisible waves called microwaves. The microwave energy is distributed throughout the oven by a rotating blade or stirrer located above a plastic cover at the top of the oven.
The oven liner is formed of metal as metal serves as a reflector of microwaves to distribute the heat energy. Certain materials allow microwaves to pass through without becoming heated, such as glass, glass ceramics, paper and the like. These materials make good food containers. Other materials, such as most foods, absorb microwaves which produces heat within the food by causing the vibration of the food molecules.
Microwave cooking differs from conventional radiant energy cooking. In conventional oven cooking, either gas or electric, heat is applied around the outside of the food by radiant energy or convection heat, and the heat is slowly transferred to the inside. When cooking with microwave energy, the food is cooked from the inside out. The oven cooking cavity does not heat up like a conventional oven. Although in a microwave oven the food does get hot and this heat is transferred to the food container. Thus it is important that the food container be supported by a shelf which can withstand high temperatures.
Most microwave oven shelves are made of glass ceramic plates which are located in the bottom of the oven cooking cavity. Since the food does get hot, food spatters do occur and water vapor does rise from the food and they may soil the walls forming the oven cooking cavity. Since the oven walls are not heated, the soil tends to run down and accumulate on the shelf or beneath the shelf on the bottom wall of the oven liner.
This liquid accumulation on the bottom of the metal oven liner is very objectionable because it attacks the welded corners or seams of the box-like oven liner and rust or corrosion may occur. The conventional solution is to provide a silicone seal around the edge of the glass-ceramic shelf to seal the gap between the shelf and vertical wall portions of the oven cooking cavity.
This presents a problem in replacing the glass-ceramic shelf upon breakage since it is sealed in place. Also it is easier to maintain the cleanliness of the shelf if it can be removed from the oven and cleaned in the sink.